As mother and son serial killers lovingly discussed their choice of methods for last week's grisly undertaking, Maureen Sowerbutts turned to David and suggested barbecuing this particular victim with red onions. "Mum," David protested. "That's disgusting! You know I don't like red onions."

This Thursday, Psychoville – the latest comedy-horror from Reece Shearsmith and Steve Pemberton, half of the team behind the gets-better-every-time-you-watch-it League of Gentlemen – reaches its deadly and disturbing denouement. Over the course of its seven-week run, the series has increasingly played out like an if-only collaboration between Alfred Hitchcock and Alan Bennett, though Norman Bates is a run-of-the-mill motel owner compared with the characters on show here.

Has there ever been a more disturbing depiction of the parent-child bond than David and Maureen Sowerbutts? Until last week, the answer would undoubtedly have been no. But then, with perfect TV timing, along came Young, Dumb and Living off Mum, a reality show so truly terrifying and terrifyingly true that it makes the residents of Psychoville look like the inhabitants of Camberwick Green.

On paper, the idea doesn't sound promising: take eight spoilt brats who've sponged off their parents all their lives, put them in a house together and then send them out into the working world to be judged by their mums and dads and voted off one by one. In reality, this Big Brother meets The Simple Life meets The Apprentice for the unemployable is pure TV gold.

In a ghostly echo of David Sowerbutts' reaction to red onions, 18-year-old "tantrum queen" Danielle stamped her feet as she screamed at her mother, "I don't like beans, you know I don't. Get me s'ghetti." Later, as one of the more capable youngsters attempted to show her how to "cook" beans for herself, the realisation slowly dawned that she had no idea how to turn a gas hob on. "The little black dots show you which ring will light up," her instructor gently pointed out as she gingerly attempted not to break a fingernail.

Danielle was not even the worst of them. Nicola, 25, gamely announced: "Jobs depress me. They depress me. The world works to get what they want. I work hard getting money out of Mum." Five minutes into the task of serving breakfast to guests at a London hotel, Nicola was turning to the camera and complaining of stress in a desperate bid for our sympathy.

Best of all, though, were the comedic double act of Dogan, 20, and Dina, 17. Dogan, who told the hotel manager who was employing him, for the day, "you'll never work for my dad," and stormed out muttering "div", and Dina, who, when told the group would be picked up at 6.15am, complained that that would mean getting up at 4.30 to do her hair. Exactly how it can take the best part of two hours to end up with a style that is best described as a crusty Dusty Springfield, was never explained, but then the series' narrator, Robert Webb, was too busy spouting cutting and sardonic asides to worry about such minor details.

Despite its Five-style title, what Young, Dumb and Living off Mum proves is that reality TV has now come full circle – from insightful documentaries to light entertainment and back again. Were Desmond Morris or Oliver James in charge of the voice-over, this would be a state-of-the-nation address to horrify those fabled Islington dinner parties. Tucked away as it is on a Beeb backwater, it is doomed to become merely word-of-mouth cult viewing for those with Gandhi-like levels of patience and stomachs strong enough for Psychoville.

Which raises the question: how would David Sowerbutts fare here? The most chilling thing of all is that, among this lot, he'd seem perfectly normal.